5,070 research outputs found
Evolution of iron core white dwarfs
Recent measurements made by Hipparcos (Provencal et al. 1998) present
observational evidence supporting the existence of some white dwarf (WD) stars
with iron - rich, core composition. In this connection, the present paper is
aimed at exploring the structure and evolution of iron - core WDs by means of a
detailed and updated evolutionary code. In particular, we examine the evolution
of the central conditions, neutrino luminosity, surface gravity,
crystallization, internal luminosity profiles and ages. We find that the
evolution of iron - rich WDs is markedly different from that of their carbon -
oxygen counterparts. In particular, cooling is strongly accelerated as compared
with the standard case. Thus, if iron WDs were very numerous, some of them
would have had time enough to evolve at lower luminosities than that
corresponding to the fall - off in the observed WD luminosity function.Comment: 8 pages, 21 figures. Accepted for publication in MNRA
Invariant manifolds and orbit control in the solar sail three-body problem
In this paper we consider issues regarding the control and orbit transfer of solar sails in the circular restricted Earth-Sun system. Fixed points for solar sails in this system have the linear dynamical properties of saddles crossed with centers; thus the fixed points are dynamically unstable and control is required. A natural mechanism of control presents itself: variations in the sail's orientation. We describe an optimal controller to control the sail onto fixed points and periodic orbits about fixed points. We find this controller to be very robust, and define sets of initial data using spherical coordinates to get a sense of the domain of controllability; we also perform a series of tests for control onto periodic orbits. We then present some mission strategies involving transfer form the Earth to fixed points and onto periodic orbits, and controlled heteroclinic transfers between fixed points on opposite sides of the Earth. Finally we present some novel methods to finding periodic orbits in circumstances where traditional methods break down, based on considerations of the Center Manifold theorem
Vere-Jones' Self-Similar Branching Model
Motivated by its potential application to earthquake statistics, we study the
exactly self-similar branching process introduced recently by Vere-Jones, which
extends the ETAS class of conditional branching point-processes of triggered
seismicity. One of the main ingredient of Vere-Jones' model is that the power
law distribution of magnitudes m' of daughters of first-generation of a mother
of magnitude m has two branches m'm with
exponent beta+d, where beta and d are two positive parameters. We predict that
the distribution of magnitudes of events triggered by a mother of magnitude
over all generations has also two branches m'm
with exponent beta+h, with h= d \sqrt{1-s}, where s is the fraction of
triggered events. This corresponds to a renormalization of the exponent d into
h by the hierarchy of successive generations of triggered events. The empirical
absence of such two-branched distributions implies, if this model is seriously
considered, that the earth is close to criticality (s close to 1) so that beta
- h \approx \beta + h \approx \beta. We also find that, for a significant part
of the parameter space, the distribution of magnitudes over a full catalog
summed over an average steady flow of spontaneous sources (immigrants)
reproduces the distribution of the spontaneous sources and is blind to the
exponents beta, d of the distribution of triggered events.Comment: 13 page + 3 eps figure
New possibility of the ground state of quarter-filled one-dimensional strongly correlated electronic system interacting with localized spins
We study numerically the ground state properties of the one-dimensional
quarter-filled strongly correlated electronic system interacting
antiferromagnetically with localized spins. It is shown that the
charge-ordered state is significantly stabilized by the introduction of
relatively small coupling with the localized spins. When the coupling becomes
large the spin and charge degrees of freedom behave quite independently and the
ferromagnetism is realized. Moreover, the coexistence of ferromagnetism with
charge order is seen under strong electronic interaction. Our results suggest
that such charge order can be easily controlled by the magnetic field, which
possibly give rise to the giant negative magnetoresistance, and its relation to
phthalocyanine compounds is discussed.Comment: 5pages, 4figure
Experimental demonstration of four-party quantum secret sharing
Secret sharing is a multiparty cryptographic task in which some secret
information is splitted into several pieces which are distributed among the
participants such that only an authorized set of participants can reconstruct
the original secret. Similar to quantum key distribution, in quantum secret
sharing, the secrecy of the shared information relies not on computational
assumptions, but on laws of quantum physics. Here, we present an experimental
demonstration of four-party quantum secret sharing via the resource of
four-photon entanglement
Asynchronous Graph Pattern Matching on Multiprocessor Systems
Pattern matching on large graphs is the foundation for a variety of
application domains. Strict latency requirements and continuously increasing
graph sizes demand the usage of highly parallel in-memory graph processing
engines that need to consider non-uniform memory access (NUMA) and concurrency
issues to scale up on modern multiprocessor systems. To tackle these aspects,
graph partitioning becomes increasingly important. Hence, we present a
technique to process graph pattern matching on NUMA systems in this paper. As a
scalable pattern matching processing infrastructure, we leverage a
data-oriented architecture that preserves data locality and minimizes
concurrency-related bottlenecks on NUMA systems. We show in detail, how graph
pattern matching can be asynchronously processed on a multiprocessor system.Comment: 14 Pages, Extended version for ADBIS 201
Tunable Vibrational Band Gaps in One-Dimensional Diatomic Granular Crystals with Three-Particle Unit Cells
We investigate the tunable vibration filtering properties of one-dimensional
diatomic granular crystals composed of arrays of stainless steel spheres and
cylinders interacting via Hertzian contact. The arrays consist of periodically
repeated three-particle unit cells (steel-cylinder-sphere) in which the length
of the cylinder is varied systematically. We apply static compression to
linearize the dynamic response of the crystals and characterize their linear
frequency spectrum. We find good agreement between theoretical dispersion
relation analysis (for infinite systems), state-space analysis (for finite
systems), and experiments. We report the observation of up to three distinct
pass bands and two finite band gaps and show their tunability for variations in
cylinder length and static compression
Deformation effect on total reaction cross sections for neutron-rich Ne-isotopes
Isotope-dependence of measured reaction cross sections in scattering of
Ne isotopes from C target at 240 MeV/nucleon is analyzed by
the double-folding model with the Melbourne -matrix. The density of
projectile is calculated by the mean-field model with the deformed Wood-Saxon
potential. The deformation is evaluated by the antisymmetrized molecular
dynamics. The deformation of projectile enhances calculated reaction cross
sections to the measured values.Comment: 6 pages, 4 figures, 2 table
Hierarchy of Temporal Responses of Multivariate Self-Excited Epidemic Processes
We present the first exact analysis of some of the temporal properties of
multivariate self-excited Hawkes conditional Poisson processes, which
constitute powerful representations of a large variety of systems with bursty
events, for which past activity triggers future activity. The term
"multivariate" refers to the property that events come in different types, with
possibly different intra- and inter-triggering abilities. We develop the
general formalism of the multivariate generating moment function for the
cumulative number of first-generation and of all generation events triggered by
a given mother event (the "shock") as a function of the current time . This
corresponds to studying the response function of the process. A variety of
different systems have been analyzed. In particular, for systems in which
triggering between events of different types proceeds through a one-dimension
directed or symmetric chain of influence in type space, we report a novel
hierarchy of intermediate asymptotic power law decays of the rate of triggered events as a function of the
distance of the events to the initial shock in the type space, where for the relevant long-memory processes characterizing many natural
and social systems. The richness of the generated time dynamics comes from the
cascades of intermediate events of possibly different kinds, unfolding via a
kind of inter-breeding genealogy.Comment: 40 pages, 8 figure
Possibility of f-wave spin-triplet superconductivity in the CoO superconductor: a case study on a 2D triangular lattice in the repulsive Hubbard model
Stimulated by the recent finding of NaCoO.1.3HO
superconductor, we investigate superconducting instabilities on a 2D triangular
lattice in the repulsive Hubbard model. Using the third-order perturbation
expansion with respect to the on-site repulsion , we evaluate the linearized
Dyson-Gor'kov equation. We find that an -wave spin-triplet pairing is the
most stable in a wide range of the next nearest neighbor hopping integral
and an electron number density . The introduction of is crucial to
adjust the van Hove singularities to the neighborhood of the Fermi surface
crossing around K point. In this case, the bare spin susceptibility shows the
broad peak around point. These conditions stabilize the -wave
pairing. Although the -wave pairing is also given by the
fluctuation-exchange approximation, the transition temperature is too low to be
observed. This is because the depairing effect by the spin fluctuation is
over-estimated. Thus, the third-order vertex corrections are important for the
spin-triplet superconductivity, like the case in SrRuO.Comment: 4 pages, 7 figure
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